In control of a hard disc drive (HDD), a touchdown measurement is known as one process for controlling a gap (the flying height of a head) between a head and a disk. The touchdown measurement is a method of applying power to the heating element (heater) of a head to thermally expand part of the head so as to protrude it to a disk and to contact it with the disk, thereby measuring applied power (i.e., a control value for the flying height) when the contact with the disk has been detected.
In general, in the touchdown measurement, a most likelihood value is calculated as a real value, based on measured values acquired by a plurality of trials. If power exceeding the real value is applied, the head may contact the disk, which may well be a cause of a head failure or reduction of reliability of the device.
Different head flying heights are detected among different heads and/or among positions on the writing surface of each disk. Therefore, in an HOD manufacturing process, touchdown measurement may be executed for each head or each disk writing surface. In this case, it is necessary to divide the disk into a plurality of radial measurement areas, and to execute touchdown measurement in each measurement area to thereby measure a flying height flying profile) therein.